An endoscope is an optical instrument for viewing and examining the interior of an organ within the human body. Broadly, an endoscope comprises a long thin tube within which are housed fiber optic elements for transmitting light to the interior regions to be viewed, and image forming and relay optical elements for transmitting an optical image to an eyepiece outside the body for viewing by the examining physician. In use, the endoscope is typically oriented with its axis pointing in a generally horizontal direction, and the physician wiggles it around to view different interior portions.
It is desirable in many circumstances to have the optical image from the endoscope fed to a television camera for viewing by more than one person or for video recording thereof. Currently, tube type television cameras are the only type in widespread use. However, even when the head of a tube type television camera is separated from the remaining portions, it represents a sizeable weight. Thus, it is not practical to directly couple a television camera to a rigid endoscope disposed within a patient without providing some sort of support mechanism for the camera.
It is known to suspend a television camera head by a cable from a pulley or a microphone boom. The camera head represents a cylindrical body, generally symmetric about its optical axis. Accordingly, the camera is suspended pointing downward (optical axis vertical) and an optical coupler between the generally horizontal endoscope and the camera must be provided. The coupler typically includes a beam splitter for simultaneous direct and television viewing. A camera relay tube is also normally used to keep the camera (which cannot be sterilized) as far from the sterile field as possible.
Even if it is possible to insert the endoscope into the patient horizontally, it is generally required that rotations and translations in three dimensions be made in the course of examination. Rotations arise as the physician moves the eyepiece end of the endoscope, so that the endoscope pivots about a point generally defined by surrounding body tissue. These rotations include rotations about the endoscope's own axis (hereinafter roll axis), rotations about a horizontal axis perpendicular to the endoscope axis (hereinafter pitch axis), and rotations about an axis perpendicular to the pitch and roll axes (hereinafter yaw axis). If a rigid coupler with a deflection mirror is used, it can be appreciated that the endoscope may be translated vertically, and may be translated horizontally so long as the angle of the suspension cable with respect to the vertical remains small. Additionally, the endoscope may be rotated about the suspension cable without placing any of the camera weight on the eyepiece end of the endoscope. However, it is impossible to rotate the endoscope about the pitch and roll axes.
Roll rotation of the endoscope is typically accommodated by providing the coupler with a bearing between the endoscope and the deflection mirror. Additionally, rotation about the pitch axis may be provided by adding a second mirror to the coupler. The first mirror is placed to produce a 90.degree. deflection about an axis parallel to the yaw axis so that light emerges horizontally parallel to the pitch axis, thus defining a coupler optical axis. The second mirror is placed to provide a 90.degree. vertical deflection to the television camera. A bearing between the two mirrors accommodates relative rotation about the coupler optical axis.
Unfortunately, the type of coupler described above results in undesirable image rotation when the endoscope is rotated in such a manner that the first mirror rotates relative to the second. That is, as the examining physician manipulates the endoscope to scan different portions of the organ being viewed, rotation of the endoscope about the pitch axis causes the image on the television screen to rotate. The standard way of handling such image rotation is the placement of a rotatable Dove prism in the camera relay system between the coupler and the television camera. Since rotation of the Dove prism causes a rotation of the image seen on the television screen, image rotation may be at least partly compensated by having an operator view the television monitor and appropriately rotate the prism. This system is still far from optimal, since even the most experienced operator is unable to completely eliminate disconcerting image rotation. Moreover, the required presence of a second person within the sterile field in close proximity to the examining physician is inconvenient at best, hazardous at worst.
Accordingly, when it is required to provide television viewing of the results of endoscopic examination procedures where the examining physician has to rotate the endoscope about all three axes, the choice has been between having an extra operator immediately nearby or putting up with disconcerting image rotation on the television screen.